Input Director is designed for those folks that have two (or more) Windows systems set up at home. Using Input Director, you can position the monitors of your systems side-by-side and then control all of them via one keyboard/mouse. To transition which system you're controlling is as simple as moving the cursor off the screen on one system and it'll pop up on the next screen (similar to a multi-monitor setup) or via a hotkey combo.

Input Director also lets you share clipboard contents, so you can copy from one machine, switch over to another and then paste. This also works for files that are in network shared directories.